Devices for automatically identifying (tracing) the number of a telephone from which a call originates do not comprise a new art, per se. Call tracing devices of various types have been in use for years by the telephone company. Prior to the present invention, however, these devices have been difficult to implement, slow in operation, and unreliable. These shortcomings, coupled with the advent of the 911 and Enhanced 911 emergency systems, have made it apparent that a need exists for a way to automatically and specifically identify any telephone within a specified geographic area from which a call is being made, especially extensions of Private Branch Exchanges (PBXs). This latter capability is particularly needed because, at the time of the present invention, all telephone trunk lines which connect the PBXs of multi-line entities such as universities, hospitals patent number, etc., to a Telephone Company's (TELCO) Central Office (CO) are identically labelled with only the primary number which has been assigned to the PBX of that institution. This means that all extensions of such a multi-line PBX are identified with the same phone number; no extension telephones can be individually identified. Thus, emergency personnel might be delayed for hours in locating the source of a call for help which originated at an extension telephone.
Furthermore, a need also exists for a means of quickly and reliably identifying the telephone numbers associated with other call originating telephones which are not associated with PBXs, including but not limited to "cordless" radio telephones and cellular telephones, for instance.
Accordingly, it is a principal object of the present invention to provide a system which includes devices capable of being installed either at a called point, such as the Public Safety Answering Point (PSAP), or a calling point, such as a PBX, or both, and which will automatically provide the number and location within a specified geographic area of a telephone from which a call is originating, especially including PBX extensions.
Throughout this Application, the term "PBX" will be used generically to represent the terms Private Branch Exchange, Private Automatic Branch Exchange, Centrex, Key System, Electronic Solid State eXchange, or commercial manufacturer's brands of telephone systems.
Known prior art pertaining to the present invention includes Letters Patent granted to Anderson, et al, U. S. Pat. No. 3,967,073, Pankonen, et al, U.S. Pat. No. 4,893,325, and Oliver, U.S. Pat. No. 4,839,917.
The device of Anderson et al, hereinafter Anderson, while possessing some of the functions of the present invention, yet lacks certain important features, most notably the ability to seek alternate routes for completing -..) an emergency 911 call if the selected line is unresponsive. Indeed, in at least his first claim is included the limitating language "means including said memory for inhibiting said selecting means when said memory has reached its storage capacity and is unable to store additional call identity information..."
Further, Anderson teaches a requirement for two lines to complete any call, one for the caller's voice transmission, and another for the ALI data. His teaching does not include any provision for the current state of the art telephones which use radio frequencies, nor any ability to code a key for use as a "panic button". Another limitation of the Anderson device is the lack of a decoding process to distinguish between a "dial 9" request to a PBX for an outside line, and an emergency 911 call in a situation when every second may count.
The system described by Pankonen et al, hereinafter Pankonen, is for an improved version of an entire PSAP station, instead of simply a complementary device for use therewith and behind PBXs. The title of the patent granted to Pankonen is an "Integrated Public Safety Answering Point System". Pankonen deals with improving the larger system and has no teaching or provision for identifying an individual extension of a PBX.
Similarly, the line status monitoring system of Oliver is a large and sophisticated system for monitoring the status of a great many telephones and reporting the activity of each to a central computer. Very few, if any, of the PBX owners/users targeted by the device of the present invention could afford or justify such an elaborate system. Therefore, such a system, being unaffordable and, thus, uninstalled and unutilized, does not represent a workable solution to the problem addressed by the present invention. Moreover, while the system of Oliver could report various alarm situations, if such a system were installed, the simple act of dialing a nine and two ones to reach a PSAP, especially the PSAP appropriate to the caller, is not addressed in his teaching. Rather, all monitored phone events, which are identified as alarms, go to an associated computer.